Project III:Mechanisms Governing the Oocyte-to-Embryo Transition John J. Eppig, Project Leader The primary objective of oocyte development is to become an embryo, one capable of development to healthy offspring. Successful oocyte-to-embryo transition depends upon the completion of meiosis and the utilization of maternal factors stored during oocyte development. This ReproGenomics Program Project has produced three infertile mutants that are unable to complete this transition and, therefore, present excellent opportunities to discover novel mechanisms that control it. Meiotic arrest 1 (marfl) mutant oocytes are unable to undergo germinal vesicle breakdown (GVB) and are ovulated at the immature (GV) stage. Oocyte maturation defective (omdl) and bromodomain and WD repeat domain containing 1 (Brwdl) mutant eggs cannot develop beyond the 2 pronuclear stage after insemination. The marfl and omdl mutations affect only females, while the Brwdl mutation affects both males and females. Aim 1 is to discover new pathways regulating the GV-to-GVB transition. The gene harboring the marfl mutation does not encode a component of maturation promoting factor (MPF), or any of its known proximal regulators. Hypotheses that MARF1 protein is either a previously unknown regulator of MPF activity or a key oocyte- specific component of pathways regulated by MPF will be tested. In Aim 2, ovulated GV-arrested marfl mutant oocytes, and oocyte culture systems, will be used to test the hypothesis that some aspects of cytoplasmic maturation, particularly the degradation of specific groups of transcripts during the GV-to-MII transition, and processes that prepare for egg activation, occur independently of nuclear maturation. Aim 3 is to discover new pathways regulating the oocyte-to-embryo transition using the Brwdl and omdl mutations, and a knockout of the oocyte-specific gene zygotic arrest 1 (Zar1) gene. The hypothesis that BRWD1, ZAR1, and OMD1 proteins are fundamental determinants of oocyte quality and that mutant alleles of genes encoding them disrupt key pathways needed to transit from GV-stage oocyte to preimplantation embryo will be tested. Relevance to Public Health: By discovering novel mechanisms controlling the oocyte-to-embryo transition, this work will provide insight into common human female infertility syndromes. The studies proposed here will discover molecules, pathways, and processes needed to produce "good" eggs capable of maturation and undergoing early embryogenesis.